Mention that 'weave launch' now waits

site/using-weave/awsvpc.md

@@ -73,6 +73,11 @@ your cluster.
 - AWS-VPC mode does not inter-operate with other Weave Net modes; it
   is all or nothing.  In this mode, all hosts in a cluster must be AWS
   instances. (We hope to ease this limitation in future.)
+- The `weave launch` command waits until the
+  [IP address manager](/site//operational-guide/concepts.md#ip-address-manager-ipam)
+  is ready, i.e. until after this peer has been able to make contact
+  with other peers and confirm that it has joined the cluster the
+  bridge.  Without AWS-VPC, `weave launch` returns without waiting.
 - The AWS network does not support multicast.
 - The number of hosts in a cluster is limited by the maximum size of
   your AWS route table.  This is limited to 50 entries though you